Utility: 1) Diagnostic screen for hemophagocytic lymphohistiocytosis.
2) Functional evaluation of natural killer (NK) function.
Specimen: 8 - 15 mL peripheral blood in sodium heparin (green top).
CPT codes: 86849, 88187.
Clinical indication/general description
Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening disorder characterized by excessive lymphocytic activation and cytokine secretion, macrophage activation, subsequent hemophagocytosis of blood cells and organ dysfunction. This disorder usually is triggered by viral infections and typically presents at a young age. All known genetic mutations associated with HLH occur in genes encoding proteins required to kill virally infected cells. Perforin, a pore-forming protein stored in cytotoxic granules and secreted by NK cells and cytotoxic CD8+ lymphocytes, is required to kill virally infected and malignant cells. Mutations in perforin or other granule associated proteins cause HLH. Individuals with HLH exhibit defective NK cell function. In addition, defective NK cell function may be seen in patients with recurrent, severe viral infections, particularly infections with herpes viruses.
A functional flow cytometric-based assay is used to evaluate the ability of a patient's NK cells to induce apoptosis of a target cell population. Target cells (K562) are fluorescently labeled to differentiate them from the patient's peripheral blood mononuclear cells. PBMCs containing NK cells (such as effectors) are cultured with target cells at different effector to target cell ratios. Target cell apoptosis is measured by incorporation of the fluorescent dye 7-AAD, which binds to the DNA in apoptotic cells. The cytotoxicity/apotosis assay will detect defects in NK cell function in patients with clinical symptoms of HLH, and it also can be used to test the function of NK cells in patients with severe or chronic viral infections.